1. Field of the Invention
The present invention relates to a sputtering apparatus, and a process for forming a lamination film employing the sputtering apparatus. More particularly, the present invention relates to a sputtering apparatus which is capable of effectively forming a lamination film of a magnetic thin film and a non-magnetic thin film, and a process for forming a lamination film employing the sputtering apparatus.
In recent magnetic recording, the magnetic thin film for use for the recording medium and the magnetic head is desired to be improved further to achieve higher reliability and higher recording density. In particular, in forming a magnetic thin film, high efficiency is desired to mass-produce of recording mediums and magnetic heads.
Hitherto, magnetic thin films have been formed by use of a diode sputtering apparatus such as the one described in Japanese Patent Publication No. 61-61164. Such sputtering apparatuses form films only at a low speed, and are not suitable for mass-production of magnetic thin films.
On the other hand, magnetron sputtering apparatuses have come to be used widely for formation of thin semiconductor films because of the high film forming speed. In this apparatus, high speed film formation is made feasible by raising the density of plasma around the target by utilizing a magnetic field which is generated by a magnet placed on the backside of the target. However, even with this apparatus, if a magnetic material is used as the target, the magnetic fluxes penetrate through the target to decrease flux leakage around the target disadvantageously, resulting in no increase in the plasma density and the film formation speed.
Counterposing target type sputtering apparatuses are reported to offset the above disadvantages (see Ohyo Butsuri (Applied Physics), Vol. 48, No. 6, (1979), pp. 558-559; and Japanese Patent Publication Nos. 63-43465, 61-60908, and 63-20304). FIG. 6 illustrates a schematic diagram of such a type of apparatus. In the apparatus as shown in FIG. 6, a pair of targets t.sub.1 and t.sub.2 are placed with their sputtering faces t.sub.1S and t.sub.2S counterposed across the space S. Magnetic field-generating means h.sub.1 and h.sub.2 are provided to generate a magnetic field H in a direction perpendicular to the sputtering faces t.sub.1S and t.sub.2S. A substrate 625 is set on a holder 626 which is placed on the lateral side of the space S between the target to form a film on the surface of the substrate. With this apparatus, a film can be formed at a low temperature at a high speed. More specifically, in FIG. 6, if a magnetic field H of from 300 to 500 Oe is generated in a direction perpendicular to the sputtering surfaces t.sub.1S and t.sub.2S, high-energy electrons emitted from the sputtering surfaces t.sub.1S and t.sub.2S are enclosed within the space between the counterposed targets. Accordingly, a number of the electrons do not reach the substrate 625, so that an ion-focusing electric field is not formed, whereby ionization of the sputtered gas is accelerated and sputtering speed is raised. Furthermore, since collision of the electrons against the substrate 625 is negligible, the temperature of the substrate does not rise significantly.
However, in formation of a lamination film composed of a magnetic thin film and a non-magnetic thin film as described in Japanese Patent Publication No. 54-3238 and Japanese Patent Application Laid-Open Nos. 60-205808 and 61-3311, etc., or a lamination film composed of a magnetic thin film and a non-magnetic thin film for a magnetic head as described in Japanese Patent Application Laid-Open No. 60-47215, the aforementioned conventional sputtering apparatuses need an additional apparatus or a vacuum chamber for forming a non-magnetic thin film. Therefore, in the case where magnetic thin films and non-magnetic films are laminated alternately, the substrate holder needs to be moved between the apparatuses or a vacuum chambers, which requires large apparatus construction, raising the apparatus cost, causing loss of time for the holder movement, and raising the production cost of the lamination film. If the substrate is exposed to the outer air during the movement of the substrate holder, additional problem arises that the quality of the lamination film deteriorates owing to change of the film composition by oxidation or to dirt adherence.